Optical waveguide structures for an image sensor

Abstract

Trenches that are filled with a reflecting material are formed in one or more dielectric layers in an image sensor. The trenches form optical waveguide structures that surround either partially or completely each photodetector in the image sensor. Each optical waveguide structure directs light towards a respective photodetector.

1 . A method for fabricating a plurality of optical waveguides in an image sensor, wherein the image sensor includes a substrate having a plurality of photodetectors formed therein that form an imaging area, the method comprising the steps of:
 forming a dielectric layer over the imaging area;   etching a plurality of trenches in at least a portion of the dielectric layer, wherein subsets of the plurality of trenches are disposed around the edges of each photodetector; and   at least partially filling each trench with a reflecting material.   
     
     
         2 . The method of  claim 1 , wherein the step of etching a plurality of trenches in at least a portion of the dielectric layer, wherein subsets of the plurality of trenches are disposed around the edges of each photodetector comprises etching a plurality of trenches in a portion of the dielectric layer, wherein subsets of the plurality of trenches are disposed around the edges of each photodetector. 
     
     
         3 . The method of  claim 2 , further comprising repeating the steps of:
 forming another dielectric layer over the imaging area; and   etching a plurality of trenches in a portion of the other dielectric layer, wherein subsets of the plurality of trenches are disposed around the edges of each photodetector; and   at least partially filling each trench with a reflecting material.   
     
     
         4 . The method of  claim 3 , wherein the step of etching a plurality of trenches in at least a portion of the dielectric layers comprises:
 forming a mask layer over the imaging area, and patterning the mask layer to form openings in the mask layer that correspond to the locations of the plurality of trenches;   etching the plurality of trenches in at least a portion of the dielectric layer through the openings in the mask layer; and   removing the mask layer.   
     
     
         5 . The method of  claim 4 , wherein the step of forming a mask layer over the imaging area, and patterning the mask layer to form openings in the mask layer that correspond to the locations of the plurality of trenches comprises the step of forming a mask layer over the imaging area, and patterning the mask layer to form openings in the mask layer that correspond to the locations of the plurality of trenches and one or more vias. 
     
     
         6 . The method of  claim 5 , further comprising the step of etching the one or more vias in the dielectric layer through at the same time the plurality of trenches are etched in the dielectric layer. 
     
     
         7 . The method of  claim 6 , further comprising the step of filling each via with the reflecting material at the same time the plurality of trenches are at least partially filled with the reflecting material. 
     
     
         8 . The method of  claim 1 , wherein the step of etching a plurality of trenches in at least a portion of the dielectric layer comprises the step of etching a plurality of trenches through the dielectric layer. 
     
     
         9 . The method of  claim 8 , further comprising the step of etching the plurality of trenches into an underlying dielectric layer. 
     
     
         10 . The method of  claim 1 , further comprising the step of forming a plurality of etch stops prior to forming a dielectric layer over the imaging area, wherein each etch stop is formed at a location that corresponds to a locations of a respective one of the plurality of trenches. 
     
     
         11 . The method of  claim 3 , wherein the locations of the plurality of trenches formed in one dielectric layer is laterally shifted a given distance from the locations of the plurality of trenches formed in another dielectric layer. 
     
     
         12 . The method of  claim 1 , wherein the step of at least partially filling each trench with a reflecting material comprises at least partially filling each trench with a metal. 
     
     
         13 . A method for fabricating a plurality of optical waveguides in an image sensor, wherein the image sensor includes a substrate having a plurality of photosensitive areas formed therein that form an imaging area, the method comprising the steps of:
 forming a first dielectric layer over the imaging area and a second dielectric layer over the first dielectric layer;   etching a plurality of trenches through the second dielectric layer and into at least a portion of the first dielectric layer, wherein subsets of the plurality of trenches are disposed around the edges of each photosensitive area; and   at least partially filling each trench with a reflecting material.   
     
     
         14 . The method of  claim 13 , further comprising the step of forming a third dielectric layer over the second dielectric layer prior to performing the step of etching the plurality of trenches. 
     
     
         15 . The method of  claim 14 , wherein the step of etching a plurality of trenches through the second dielectric layer and into at least a portion of the first dielectric layer, wherein subsets of the plurality of trenches are disposed around the edges of each photosensitive area comprises etching a plurality of trenches through the third and second dielectric layers and into at least a portion of the first dielectric layer, wherein subsets of the plurality of trenches are disposed around the edges of each photosensitive area. 
     
     
         16 . The method of  claim 15 , wherein the step of etching a plurality of trenches through the third and second dielectric layers and into at least a portion of the first dielectric layer comprises:
 forming a mask layer over the third dielectric layer and patterning the mask layer to form openings in the mask layer that correspond to the locations of the plurality of trenches;   etching the plurality of trenches through the third and second dielectric layers and into at least a portion of the first dielectric layer through the openings in the mask layer; and   removing the mask layer.   
     
     
         17 . The method of  claim 13 , further comprising the step of forming a plurality of etch stops prior to forming a first dielectric layer over the imaging area and a second dielectric layer over the first dielectric layer. 
     
     
         18 . The method of  claim 13 , wherein the step of at least partially filling each trench with a reflecting material comprises at least partially filling each trench with a metal.